Conventional automatic noise reduction systems detect the amplitude or frequency content (or both the amplitude and frequency content) of electronic noise extracted from a noisy signal, and perform appropriate, desired, or programmed corrections on the noisy signal in response to the detected noise content. Conventional automatic noise reduction circuitry measures the noise content of an input signal, uses the measured data as feedback to adjust the parameters of conventional noise reduction circuitry automatically, and processes the input signal using the so-adjusted noise reduction circuitry.
In the field of color television signal processing, it is common to control as many as twenty-four parameters (each parameter having eight possible values) in generating and transmitting an R, G, B color television signal. Thus, the signal to noise characteristics of a color television signal may rapidly vary with time, for example as different electronic sources are employed, or scene lighting or scenery content changes occur.
Conventional automatic noise reduction circuitry is capable of responding, to a limited degree, to the changing signal to noise characteristics of a television signal without human intervention. However, the signal to noise characteristics of noise reduced output signals produced by conventional automatic noise reduction circuits are poor because such conventional circuits employ feedback signals indicative only of the average noise characteristics (over the entire frequency spectrum) of the noisy signal being processed. Thus, conventional automatic noise reduction circuitry will not vary noise reduction parameters in response to changes in the noise characteristics of the signal being processed, if such changes do not affect the average noise parameter indicated by such feedback signals.
It has not been known until the present invention how to improve the quality of the output signal of an automatic noise reduction system by independently processing the frequency components of the input signal to such system. Nor has it been known how to efficiently to employ a set of feedback signals in an automatic noise reduction system, where each feedback signal is indicative of the noise characteristics of a different frequency component of a noisy signal being processed.